(a) Field of the Invention
This disclosure relates to polylactide resin, a method of preparing the same, and a polylactide resin composition comprising the same. More particularly, this disclosure relates to polylactide resin that may exhibit and maintain excellent mechanical properties, exhibit excellent heat resistance, and thus can be used for a semi-permanent use, a method for preparing the same, and a polylactide resin composition comprising the same.
(b) Description of the Related Art
A polylactide (or polylactic acid) resin is a kind of resin comprising a repeat unit of the following General Formula. Since the polylactide resin is based on biomass unlike existing crude oil-based resin, it may utilize renewable resource, less discharge global warming gas of CO2 compared to existing resin when prepared, and has appropriate mechanical strength equivalent to the existing crude oil-based resin together with eco-friendly property such as being biodegradable by water and microorganisms, and the like when embedded.

The polylactide resin has been mainly used for a disposable packaging, coating, foam, a film/sheet and fiber, and recently, there is a growing effort to mix the polylactide resin with existing resin such as ABS, polycarbonate or polypropylene, and the like to compensate the properties, and then, apply it for a semi-permanent use such as exterior furnishing of a mobile phone or interior furnishing of automobiles, and the like. However, since the polylactide resin is difficult to manifest and maintain excellent mechanical properties due to decomposition or depolymerization, and the like during use, the application range is limited as yet.
Meanwhile, as a method of preparing existing polylactide resin, a method of direct condensation polymerization of lactic acid, or ring opening polymerization of lactide monomers in the presence of an organic metal catalyst is known. Since the direct condensation polymerization, although it may prepare inexpensive polymer, is difficult to obtain polymer of high molecular weight having weight average molecular weight of 100,000 or more, it is difficult to secure sufficient physical and mechanical properties of polylactide resin. Although ring opening polymerization of lactide monomers requires higher unit cost compared to condensation polymerization because it should prepare lactide monomers from lactic acid, it may obtain resin having relatively high molecular weight and is advantageous in terms of polymerization control, and thus, it is commercially applied.
Representative catalysts used in the ring opening polymerization may comprise an Sn containing catalyst such as Sn(Oct)2 (Oct=2-ethyl hexanoate). However, it has been reported that this catalyst tends to facilitate depolymerization under conversion rate beyond a certain level, as well as facilitate ring opening polymerization (U.S. Pat. No. 5,142,023; Leenslag et al. Makromol. Chem. 1987, 188, 1809-1814; Witzke et al. Macromolecules 1997, 30, 7075-7085). On this account, polylactide resin prepared by the ring opening polymerization is also difficult to have sufficiently high molecular weight, and it has insufficient physical, mechanical properties because thermal decomposition or hydrolysis, and the like occur due to depolymerization during use.
Thus, even if previously known ring opening polymerization is applied, it is difficult to provide polylactide resin having sufficiently high molecular weight and excellent mechanical property, and decomposition or depolymerization of resin occurs during use of the polylactide resin thus largely deteriorating mechanical property. Therefore, there is a limit in an effort to apply eco-friendly polylactide resin for a semi-permanent use such as exterior furnishing of a mobile phone or interior furnishing of automobiles.